On Fri, Feb 25, 2022 at 04:59:01PM +0000, Mark Brown wrote:
By default all SME operations in userspace will trap. When this happens we allocate storage space for the SME register state, set up the SVE registers and disable traps. We do not need to initialize ZA since the architecture guarantees that it will be zeroed when enabled and when we trap ZA is disabled.
On syscall we exit streaming mode if we were previously in it and ensure that all but the lower 128 bits of the registers are zeroed while preserving the state of ZA. This follows the aarch64 PCS for SME, ZA state is preserved over a function call and streaming mode is exited. Since the traps for SME do not distinguish between streaming mode SVE and ZA usage if ZA is in use rather than reenabling traps we instead zero the parts of the SVE registers not shared with FPSIMD and leave SME enabled, this simplifies handling SME traps. If ZA is not in use then we reenable SME traps and fall through to normal handling of SVE.
Signed-off-by: Mark Brown broonie@kernel.org
Reviewed-by: Catalin Marinas catalin.marinas@arm.com